Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art in Australia, Europe, New Zealand, the United States of America or elsewhere, on or before the priority date of the disclosure herein.
Unless stated otherwise, throughout the ensuing description, “gas” or “gases” refers to any suitable gas, mixture of gases, vapour or a gas/vapour mixture that, as such, can be monitored using the gas flow indicator device of the invention. A gas with which the flow indicator device can be used can entrain an aerosol. In the context of medical or other respiratory applications of the gas flow indicator device, “gas” refers to any suitable breathing gas, generally oxygen, a mixture of oxygen and inert gas and/or pharmacological agent, air and oxygen-enriched air. Similarly, the expression “gas delivery device”, “gas delivery system” or “gas delivery conduit” refers to any suitable device, system and conduit for supplying gas to, or at, a desired location such as, in the context of a medical or other respiratory application, to or into an individual's airway. Examples of suitable device, devices, system or conduit include, but are not limited to face masks, mouth pieces, nasal cannulas and gas supply conduits. For non-spontaneous breathing applications suitable device, devices, systems and conduits may include manual resuscitator devices, such as, for example, bag valve masks and endotracheal tubes.
Supplemental gas is widely used in the medical field. For example, supplemental oxygen is used to assist or maintain safe blood oxygen levels for a patient. The duration of supply of supplemental oxygen varies, depending on the condition of the patient and/or the particular circumstance necessitating supplemental oxygen being administered. Common scenarios include patients having a cardiorespiratory disease or dysfunction and surgical/anaesthetic intervention that mandates supplementation of atmospheric air with higher concentrations of inspired oxygen in order to achieve normal oxygen tensions in the patient's blood. Failure to deliver supplemental oxygen can lead to risk of reduced arterial oxygen tension that, if not corrected, can contribute directly to increased morbidity and mortality.
Failure of supplemental gas delivery is an acknowledged and feared system risk in hospitals. To safeguard against this, more often than not there are multilevel complex alarms and flow sensors within the hospital's in-built gas piping circuitry, and/or at gas supply outlets provided throughout hospital facilities. In addition, anaesthetic machines, intensive care ventilators, or the likes, have mandatory flow sensors engineered into their design to detect and alert of gas supply failure.
The gas supply systems of most hospitals generally are monitored, from the source to the supply outlet. The same applies to complex anaesthetic machines and ventilators. However, the most commonly used, and often most simple, gas delivery devices, systems and conduits, are not provided with any effective gas flow indicator device. Hence, their use can lead to the failure of gas delivery going unnoticed. This risk is increased in situations involving gas supply from portable gas tanks or cylinders.
One of the most commonly used gas delivery devices for spontaneously breathing patients is the gas delivery mask, or oxygen mask. Sometimes called the “Hudson Mask”, with reference to the early mask innovations of the Hudson Company, most such masks are made of a clear plastics material and include a body that is sized to seat over the nose and mouth of a patient. With conventional mask designs, gas is introduced through a gas inlet, and expiratory gases are vented from either around the side of the mask or through appropriately placed ventilation apertures. Gas is supplied to the gas inlet from a gas supply source, commonly by way of a length of clear plastic conduit. The gas supply source may be an in-built hospital supply source, or a gas tank or cylinder.
Oxygen masks usually are designed to increase a patient's inspired fraction of oxygen, such as from about 21% to about 40%. The oxygen flow rate required to achieve this is about 6 liters per minute (“6 L/min”). When oxygen flow into the mask fails the prescribed inspired oxygen concentration is not achieved. Of greater concern, the patient re-breathes their expired gases which can't be replenished satisfactorily by entrainment of air around the side of the mask, ultimately leading to the inspiration of a gas mixture with a low level of oxygen (less than 21% oxygen) and a risk of hypoxemia. Oxygen masks are not presently provided with any visual indicator confirming the presence of oxygen flow into the mask, or in the oxygen supply conduit proximate the mask. With the use of a mask, it is not inherently obvious to a medical practitioner, to a carer or even to the patient when there is an insufficient or complete lack of oxygen flow. A visual inspection of the oxygen delivery system (e.g. conduit and mask) will not generally indicate whether or not oxygen is or flowing. For this reason, medical practitioners often find it necessary to use audible cues as a means of identifying that there is a flow of oxygen. However, even putting ones ear or a stethoscope adjacent to a mask may sometimes still not make clear whether gas is flowing, and the medical practitioner still has no way of knowing whether oxygen is being supplied at the prescribed flow rate of oxygen, such as about 6 L/min.
For non-spontaneously breathing patients, one of the most commonly used manual resuscitator gas delivery devices is the bag valve mask or “BVM”. Sometimes called the “AMBU” bag or mask, with reference to the proprietary name appointed by the inventors' of the original BVM, such devices consist of a flexible air chamber (the “bag”) attached to a face mask or endotracheal tube via a shutter valve. When the mask is properly applied to a patient (or endotracheal tube is correctly inserted into the patient's trachea) and the “bag” is squeezed, the device forces air into the patient's lungs. When the bag is released, it self-inflates from its supply end, drawing in either ambient air or oxygen supplied by an oxygen supply source, while also allowing the patient's lungs to deflate to the ambient environment (but not to the “bag”) by way of a one-way expired air valve. The BVM generally includes two inlet ports for drawing in ambient air or oxygen. When available, oxygen is supplied to one of the inlet ports from a gas supply source, commonly by way of a length of clear plastic conduit. The gas supply source may be an in-built hospital supply source, or a gas tank or cylinder. The other inlet port can then be used to draw in ambient air, or to connect a reservoir for catching unused oxygen between compressions of the “bag”. In case oxygen flow is not sufficient to fill the “bag”, the reservoir generally includes a one-way valve for drawing in ambient air to ensure that the BVM continues to supply at least ambient air to the patient.
BVMs are designed to deliver up to 100% inspired oxygen to a patient. With a loss of supplemental oxygen supply into the “bag”, the BVM will continue to entrain ambient air (with an oxygen concentration of about 21%) with which to ventilate the patient. However, patients requiring the use of such manual resuscitator devices often have severely compromised respiratory function, which means that they require much higher inspired oxygen concentrations than that of ambient air. Therefore, any loss of supplemental oxygen supply can have catastrophic sequelae if undiagnosed. As with the case of the common oxygen mask described above, loss of oxygen supply to a BVM can be, and often is, missed as there is presently no visual flow indicator device provided at or proximate the BVM confirming supplemental oxygen inflow. Again, although the presence of a sound may indicate that gas is flowing, the medical practitioner still has no way of knowing whether the required flow rate of oxygen is present at the BVM.
Often gas tanks or cylinders are used to supply oxygen to masks or BVM's, most commonly in emergency, perioperative, critical care or transport scenarios. While some cylinders do have ball-type flow indicators at their supply outlets, the cylinders are often placed in positions in which they are visually obscured, such as under a patient's bed or transportation trolley, or placed side-ways rendering the ball-type flow indicators inaccurate. Additionally, most cylinders do not have alarms in the event of cylinder oxygen supply running empty during use to indicate oxygen supply failure. Even more concerning is that newer designs of oxygen cylinders commonly no longer have ball-type or other flow indicator incorporated into their design. Hence, failure of supply of supplemental gas to gas delivery devices or systems is a real and likely problem.
A substantial advance in the art is provided by the gas flow indicator device disclosed in our International Patent Application No.: PCT/AU2013/000884, published under WO 2014/026221 A1 on 20 Feb. 2014, and its counterparts in Australia (Application No.: 2013302298), Europe (Application No.: 13829326.1), New Zealand (Application No.: 705892) and the United States of America (application Ser. No. 14/421,039). The gas flow indicator device of those Applications comprises a gas flow chamber including a transparent portion and an opaque portion, an inlet port, an outlet port, and a gas flow signal means movably disposed within the gas flow chamber; wherein, when there is no gas flow or less than a predetermined gas flow rate, the gas flow signal means is disposed at least substantially within one of the transparent portion and the opaque portion; and wherein, when there is gas flow and the predetermined gas flow rate has been achieved or is being maintained, the gas flow signal means is moved to be disposed at least substantially within the other of the transparent portion and the opaque portion. Typically, the gas flow signal means is biased to a rest position substantially within the one of the transparent and opaque portions and includes a bellows device or a piston device.
While the gas flow indicator device, of our earlier patent Applications identified above, works effectively and is reliable, it is relatively complex and requires careful attention to detail in its manufacture. The present invention is concerned with providing an improved form of gas flow indicator device.